A Method to Determine the Minimum Energy Threshold and Coarse Low Energy Calibration for PVT Based Detectors Using the Lower Level Discriminator. SARAH BENDER (Juniata College Huntingdon, PA 16652) RICHARD KOUZES (Pacific Northwest National Laboratory, Richland, WA, 99352)

Radiation portal monitors (RPMs) play a critical role in ongoing attempts to intercede illicit radiological sources. RPMs widely utilize polyvinyl toluene (PVT) based detectors which have relatively high durability and low cost, but intrinsically poor energy resolution. However, a pulse height analyzer does provide some spectroscopic information allowing broad energy windowing (EW) algorithms to be employed as a complement to less specific gross count measures when detecting radiation. Quantifying the low energy sensitivity and low energy calibration of these detectors presents unique obstacles since the photon interaction in PVT is dominated by Compton scattering events, masking full energy peaks in the energy range of interest, and driving an increase in the count rate in the low energy region. A method to gauge the sensitivity of PVT detectors and generate a coarse low energy (~5keV to ~80keV) calibration by varying the lower level discriminator (LLD) setting and tracking the net count rate from a source has been investigated for several commercial PVT-based RPM systems using 55Fe, 109Cd and 241Am. Parameters in a Fermi function were adjusted to fit the resulting integral pulse height data and the derivative of the generated fit function, representing the differential pulse height spectrum, was determined. The presence of a peak in the derivative of the count rate for a source signified the presence of a photopeak, and provided a means of assessing the low energy sensitivity of the detector. Additionally, observed peaks in such differential pulse height curves for multiple sources with peaks in the 5keV to 80keV range allowed a coarse low energy calibration to be established.

Analysis of Sensor Viability for Transmission Lines in Close Proximity to Zero-Potential Grounding Objects. ALEXANDER BATALLER (University of California Santa Cruz Santa Cruz, CA 95010) DONALD HAMMERSTROM (Pacific Northwest National Laboratory, Richland, WA, 99352)

Zero-Potential Grounding Object (ZPGO) is any object that has the ability to come into contact with Transmission Lines thereby creating grounding for current. Trees are the ZPGO of focus in this study as they are the most common. In order to determine if sensors can be placed on trees that can successfully detect voltage running from Transmission Lines to ground, a quantitative analysis is needed to determine if said voltage will be detectable as a function of distance. By creating Simple Circuit, Voltage as a function of distance, Change in Swing Ratio, and Cross-Sectional Voltage Fields through a Finite Difference Method models (CSVFFDM), voltage data can be acquired using Excel and MatLab. When analyzing voltage data through these various models, the extremely low current values coupled with the high variability in tree conductivity eliminates the chances for conventional voltage readings. Further analysis in mapping CSVFFDM will provide a more accurate representation of Transmission Line models and a possibility for sensor viability on Transmission Line Poles.